Nicolas Sarkozy's UMP party has been accused of anti-Semitism after it described Dominique Strauss-Kahn, his most dangerous potential rival for re-election, as "not representing the soil of France".

The comments were part of a full-scale assault by Mr Sarkozy's right-wing allies on Mr Strauss-Kahn, currently head of the International Monetary Fund and likely presidential hopeful for the opposition Socialists.

His IMF mandate in Washington officially ends in September 2012, several months after the scheduled date of France's vote.

But there has been intense speculation that the man popularly known in France as DSK will step down early. Polls suggest he would easily win if a run-off took place now.

In recent days, UMP figures have launched a virulent pre-emptive strike against the 61-year-old, a Socialist former finance minister whom Mr Sarkozy backed to become IMF chief.

Alongside barbs that DSK, who is Jewish, was a wealthy, cosmopolitan "ultra-champagne Socialist" out of touch with his native country, the most provocative strike came from the leader of the UMP in parliament Christian Jacob, who claimed DSK did not represent "the image of France, the image of rural France, the image of French soil that we love".

Pierre Moscovici, a top DSK ally, said the attack "resembles a little the rhetoric of the far-right between the two world wars" who attacked French Jewish Socialists with similar language. "We have very well understood the rotten stench behind this declaration," said Benoît Hamon, Socialist party spokesman.

The UMP has let it be known it will not hesitate to use Mr Strauss-Kahn's allegedly colourful private life as a weapon against him. In 2008, he caused controversy at the IMF for having an affair with a young female economist.

Le Canard Enchaîné, the satirical weekly, quoted President Sarkozy as saying: "If DSK returns, scandals will come out As soon as he kicks off his (electoral) campaign, he'll be hit by Exocets".

Mr Strauss-Kahn saw his popularity in France drop by seven points according to one poll this week from pole position to number five, with a 51pc approval rating. Another poll, however, put him in first place, with 79pc compared to 37pc for President Sarkozy.